Question

With reference to stomatal movement, choose the correct statements:
[a.] Proton efflux increases pH of guard cells.
[b.] Efflux of K$^+$ and Cl$^-$ decreases water potential of guard cells.
[c.] In the absence of light, K$^+$ and Cl$^-$ efflux from guard cells.
[d.] Presence of ABA in guard cells causes efflux of K$^+$.

• A. a, b, c, d
• B. a, c, d
• C. b, c, d
• D. b, d

Hint:

Stomatal closure involves loss of K$^+$ and Cl$^-$ from guard cells, especially in dark or under ABA signals.

Answer 1

The Correct Option is B

Let’s evaluate each statement:
- (a) True: When protons (H$^+$) are pumped out of guard cells, it leads to an increase in pH inside the cell due to loss of acidity.
- (b) False: Efflux of K$^+$ and Cl$^-$ increases the water potential (i.e., becomes less negative), causing water to exit guard cells, resulting in stomatal closure.
- (c) True: In darkness, guard cells lose K$^+$ and Cl$^-$, leading to water loss and stomatal closure.
- (d) True: ABA (abscisic acid) triggers the efflux of K$^+$, contributing to stomatal closure under stress conditions like drought.
Hence, the correct statements are a, c, and d.

Answer 2

With reference to stomatal movement, choose the correct statements:

[a.] Proton efflux increases pH of guard cells.
This is correct because when protons (H⁺) are pumped out of guard cells, the pH inside increases, which is associated with stomatal closure.

[b.] Efflux of K$^+$ and Cl$^-$ decreases water potential of guard cells.
This is incorrect. The efflux (loss) of K$^+$ and Cl$^-$ ions increases the water potential inside guard cells, causing water to move out and stomata to close.

[c.] In the absence of light, K$^+$ and Cl$^-$ efflux from guard cells.
This is correct. Without light, guard cells lose K$^+$ and Cl$^-$, leading to water loss and stomatal closure.

[d.] Presence of ABA in guard cells causes efflux of K$^+$.
This is correct. Abscisic acid (ABA) triggers K$^+$ efflux, causing stomata to close during stress conditions like drought.

Correct Answer: a, c, d